Any cooled vessel can be used as a condenser and thus a piece of tube which is cooled by contact between its external surface and the surrounding air and into which hot vapour is passed will under appropriate circumstances act as a condenser. Greater efficiency is achieved by artificially cooling the tube and in the conventional Liebig condenser, the tube is surrounded by a second tube and the space between the two tubes is filled with water which is supplied to the space under pressure so as to be forced to flow therethrough and to constitute a cooling water jacket surrounding the inner tube. Such condensers have a limited thermal capacity and it is possible for the condensing operation to cease partially or completely if there is a drop in the pressure of the water supplied to the water jacket. Typical connections to the water jacket are simple push fit connections and a rise in water pressure can lead to a flooded laboratory.
Since such a condenser is usually attached to the cold water supply main, considerable variation in pressure can be expected during a 24-hour period and problems such as those outlined can become of paramount importance if an experiment has to be carried out under controlled conditions for a long period of time or if the experimental apparatus has to be left unattended.